Optical device structure using GaN substrates for laser applications

ABSTRACT

An optical device includes a gallium nitride substrate member having an m-plane nonpolar crystalline surface region characterized by an orientation of about −1 degree towards (000-1) and less than about +/−0.3 degrees towards (11-20). The device also has a laser stripe region formed overlying a portion of the m-plane nonpolar crystalline orientation surface region. In a preferred embodiment, the laser stripe region is characterized by a cavity orientation that is substantially parallel to the c-direction, the laser stripe region having a first end and a second end. The device includes a first cleaved c-face facet, which is coated, provided on the first end of the laser stripe region. The device also has a second cleaved c-face facet, which is exposed, provided on the second end of the laser stripe region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 12/868,441, filedAug. 25, 2010, which is a continuation-in-part of U.S. Ser. No.12/759,273, filed Apr. 13, 2010; which claims priority to U.S. Ser. No.61/168,926, filed Apr. 13, 2009; and U.S. Ser. No. 61/243,502, filedSep. 17, 2009, each of which is commonly assigned and herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

This invention is directed to optical devices and related methods. Moreparticularly, the invention provides a method and device for emittingelectromagnetic radiation using nonpolar gallium containing substratessuch as GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others. Theinvention can be applied to optical devices, lasers, light emittingdiodes, solar cells, photoelectrochemical water splitting and hydrogengeneration, photodetectors, integrated circuits, and transistors, aswell as other devices.

In the late 1800's, Thomas Edison invented the light bulb. Theconventional light bulb, commonly called the “Edison bulb,” has beenused for over one hundred years for a variety of applications includinglighting and displays. The conventional light bulb uses a tungstenfilament enclosed in a glass bulb sealed in a base, which is screwedinto a socket. The socket is coupled to an AC power or DC power source.The conventional light bulb can be found commonly in houses, buildings,and outdoor lightings, and other areas requiring light or displays.Unfortunately, drawbacks exist with the conventional Edison light bulb:

-   -   The conventional light bulb dissipates much thermal energy. More        than 90% of the energy used for the conventional light bulb        dissipates as thermal energy.    -   Reliability is an issue since the conventional light bulb        routinely fails often due to thermal expansion and contraction        of the filament element.    -   Light bulbs emit light over a broad spectrum, much of which does        not result in bright illumination or due to the spectral        sensitivity of the human eye.    -   Light bulbs emit in all directions and are not ideal for        applications requiring strong directionality or focus such as        projection displays, optical data storage, or specialized        directed lighting.

In 1960, the laser was first demonstrated by Theodore H. Maiman atHughes Research Laboratories in Malibu. This laser utilized asolid-state flashlamp-pumped synthetic ruby crystal to produce red laserlight at 694 nm. By 1964, blue and green laser output was demonstratedby William Bridges at Hughes Aircraft utilizing a gas laser designcalled an Argon ion laser. The Ar-ion laser utilized a noble gas as theactive medium and produce laser light output in the UV, blue, and greenwavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm,488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ion laserhad the benefit of producing highly directional and focusable light witha narrow spectral output, but the efficiency, size, weight, and cost ofthe lasers were undesirable.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green and bluelasers. As a result, lamp pumped solid state lasers were developed inthe infrared, and the output wavelength was converted to the visibleusing specialty crystals with nonlinear optical properties. A green lamppumped solid state lasers had 3 stages: electricity powers lamp, lampexcites gain crystal which lases at 1064 nm, 1064 nm goes into frequencyconversion crystal which converts to visible 532 nm. The resulting greenand blue lasers were called “lamped pumped solid state lasers withsecond harmonic generation” (LPSS with SHG) and were more efficient thanAr-ion gas lasers, but were still too inefficient, large, expensive,fragile for broad deployment outside of specialty scientific and medicalapplications. Additionally, the gain crystal used in the solid statelasers typically had energy storage properties which made the lasersdifficult to modulate at high speeds which limited its broaderdeployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal which lases at 1064 nm, 1064 nmgoes into frequency conversion crystal which converts to visible 532 nm.The DPSS laser technology extended the life and improved the efficiencyof the LPSS lasers, and further commercialization ensue into morehigh-end specialty industrial, medical, and scientific applications.However, the change to diode pumping increased the system cost andrequired précised temperature controls, leaving the laser withsubstantial size, power consumption while not addressing the energystorage properties which made the lasers difficult to modulate at highspeeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS-SHG lasers, but the specialty diodes andcrystals required make this challenging. Additionally, while thediode-SHG lasers have the benefit of being directly modulate-able, theysuffer from severe sensitivity to temperature which limits theirapplication.

From the above, it is seen that techniques for improving optical devicesis highly desired.

BRIEF SUMMARY OF THE INVENTION

This invention provides a method and device for emitting electromagneticradiation using nonpolar or semipolar gallium containing substrates suchas GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others. In a specificembodiment, the electromagnetic radiation has a wavelength of 405, 450,485, 500, 520, nanometers and others.

In a specific embodiment, the invention provides an optical device. Theoptical device includes a gallium nitride substrate member having anm-plane nonpolar crystalline surface region characterized by anorientation of about −2 degrees to about 2 degrees towards (0001) andless than about +/−0.5 degrees towards (11-20) or preferably about −1degree towards (0001) and less than about +/−0.3 degrees towards(11-20). In a specific embodiment, the crystalline surface can becharacterized as a miscut and does not include a cut orientation of zerodegrees. The device also has a laser stripe region formed overlying aportion of the m-plane nonpolar crystalline orientation surface region.In a preferred embodiment, the laser stripe region is characterized by acavity orientation that is substantially parallel to the c-direction,the laser stripe region having a first end and a second end. The deviceincludes a first cleaved c-face facet provided on the first end of thelaser stripe region. In a specific embodiment, the first cleaved c-facefacet is characterized by a laser scribed region. The device also has asecond cleaved c-face facet provided on the second end of the laserstripe region. In a specific embodiment, the second cleaved c-face facetis characterized by a laser scribed region. In a preferred embodiment,the second cleaved c-face facet is exposed, is substantially free froman optical coating, or is exposed gallium and nitrogen containingmaterial and the second cleaved c-face facet comprises a reflectivecoating. Of course, there can be other variations, modifications, andalternatives.

In a specific embodiment, the invention provides an optical device. Theoptical device includes a gallium nitride substrate member having anm-plane nonpolar crystalline surface region characterized by anorientation of about −17 degrees to about 17 degrees towards a c-plane.In a specific embodiment, the crystalline surface can be characterizedas a miscut and does not include a cut orientation of zero degrees. Thedevice also has a laser stripe region formed overlying a portion of them-plane nonpolar crystalline orientation surface region or alternativelythe semipolar crystalline orientation surface region. In a preferredembodiment, the laser stripe region is characterized by a cavityorientation that is substantially parallel to the c-direction or theprojection of the c-direction. In a preferred embodiment, the laserstripe region has a first end and a second end. The device includes afirst cleaved face facet provided on the first end of the laser striperegion. In a specific embodiment, the first cleaved face facet ischaracterized by a laser scribed region. The device also has a secondcleaved face facet provided on the second end of the laser striperegion. In a specific embodiment, the second cleaved face facet ischaracterized by a laser scribed region. In a preferred embodiment, thefirst cleaved facet comprises a reflective coating and the secondcleaved facet comprises no coating, an antireflective coating, orexposes gallium and nitrogen containing material.

In an alternative specific embodiment, the invention provides a methodfor forming an optical device. The method includes providing a galliumnitride substrate member having an m-plane nonpolar crystalline surfaceregion characterized by an orientation of about −2 degrees to about 2degrees towards (0001) and less than about 0.5 degrees towards (11-20)or preferably about −1 degree towards (0001) and less than about +/−0.3degrees towards (11-20). In a specific embodiment, the crystallinesurface can be characterized as a miscut and does not include a cutorientation of zero degrees. The device also has a laser stripe regionformed overlying a portion of the m-plane nonpolar crystallineorientation surface region. In a specific embodiment, the laser striperegion is characterized by a cavity orientation substantially parallelto the c-direction. In a specific embodiment, the laser stripe regionhas a first end and a second end. The method preferably forms a pair ofcleaved facets including a first cleaved c-face facet provided on thefirst end of the laser stripe region and a second cleaved c-face facetprovided on the second end of the laser stripe region.

In other embodiments, the invention includes a device and methodconfigured on other gallium and nitrogen containing substrateorientations. In a specific embodiment, the gallium and nitrogencontaining substrate is configured on a family of planes including a{20-21} crystal orientation. In a specific embodiment, {20-21} is 14.9degrees off of the m-plane towards the c-plane (0001). As an example,the miscut or off-cut angle is +/−17 degrees from the m-plane towardsc-plane or alternatively at about the {20-21} crystal orientation plane.As another example, the present device includes a laser stripe orientedsubstantially in a projection of the c-direction, which is perpendicularto the a-direction (or alternatively on the m-plane, it is configured inthe c-direction). In one or more embodiments, the cleaved facet would bethe gallium and nitrogen containing face (e.g., GaN face) that is +1-5degrees from a direction orthogonal to the projection of the c-direction(or alternatively, for the m-plane laser, it is the c-face). Of course,there can be other variations, modifications, and alternatives.

In further specific embodiment, the invention provides a laser devicecomprising a gallium and nitrogen containing substrate having a surfaceregion configured in a non-polar orientation, an active regioncomprising a plurality of quantum well regions and at least a pair ofthin barrier regions configured on each of the sides of at least one ofplurality of quantum well regions. That is, the quantum well region issandwiched between the pair of barrier region in a specific embodiment.

In a specific embodiment, the invention provides a laser devicecomprising a gallium and nitrogen containing substrate having a surfaceregion configured in a non-polar orientation, an active regioncomprising at least five quantum well regions and at least four thinbarrier regions configured to separate respective first quantum wellregion, second quantum well region, third quantum well region, fourthquantum well region, and fifth quantum well region. That is, a firstbarrier region separates the first from the second quantum well region,a second barrier region separates the second quantum well region fromthe third quantum well region, a third barrier region separates thethird quantum well region from the fourth quantum well region, and thefourth barrier region separates the fourth quantum well region from thefifth quantum well region. In a preferred embodiment, each of thebarrier regions is thin and is characterized by a thickness of 2.5 nmand less, which leads to reduced overall strain in the active regionincluding both the quantum well regions and barrier regions. As usedherein, the second, third, and fourth quantum well regions areconfigured within the first and fifth quantum well regions, which areconfigured within a vicinity of exterior portions of the active region.Of course, one of ordinary skill in the art would recognize that theremay be more than five quantum well regions or fewer than five quantumwell regions.

Moreover, the invention provides a gallium and nitrogen containingoptical device comprising a gallium and nitrogen containing substratecomprising a surface region configured in a semi-polar {20-21}orientation; an active region comprising a plurality of quantum wellregions and at least a pair of thin barrier regions configured onrespective sides of at least one of the plurality of quantum wellregions; and a laser stripe region configured in a projection of ac-direction.

The present invention enables a cost-effective optical device for laserapplications. In a specific embodiment, the present optical device canbe manufactured in a relatively simple and cost effective manner.Depending upon the embodiment, the present apparatus and method can bemanufactured using conventional materials and/or methods according toone of ordinary skill in the art. The present laser device uses anonpolar gallium nitride material capable of achieving a laser having awavelength of about 400 nanometers to about 500 nanometers and greater,among others. In other embodiments, the device and method can achieve awavelength of about 500 nanometers and greater including 520 nanometersto about 540 nanometers. In a specific embodiment, the method and devicecan achieve a wavelength of 435 to 470 nanometers, among others. In apreferred embodiment, the single lateral mode laser device ischaracterized by a wall plug efficiency (optical power out/electricalpower in) of about 14-25% in the 50 to 150 mW output power range for alaser configured on a non-polar gallium and nitrogen containingmaterial. The wall plug efficiency of the single lateral mode laserdevice can be characterized by values greater than 20%. In suchembodiments, the electrical power may range from about 50 mW to about200 mW and can be greater such as 200 mW to about 500 mW and can beothers. In other embodiments, the present laser device configured on asemi-polar substrate orientation (e.g., {20-21}, slightly offcut{20-21}) provides wall plug efficiencies of 6% to 12% and greater foremission of 520 nanometers and greater. In a specific embodiment, thepresent device can be configured as a single lateral mode or multi-modedevices. In a preferred embodiment, the present single lateral modedevice has a wall plug efficiency of 15 to 25% and may be at least 1.5to 2× higher than conventional single lateral mode devices operating inthe 435 to 470 nanometer range. In a preferred embodiment, the presentlaser devices uses a multi-quantum well structure configured with thinbarrier regions for improved device performance, including higher wallplug efficiency and desirable other desirable electrical properties.Depending upon the embodiment, one or more of these benefits may beachieved. These and other benefits may be described throughout thepresent specification and more particularly below.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the latter portions of thespecification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of a laser device fabricated ona nonpolar substrate according to an embodiment of the presentinvention;

FIG. 2 is a detailed cross-sectional view of a laser device fabricatedon a nonpolar substrate according to an embodiment of the presentinvention;

FIG. 3 is a cross-sectional view photograph of a c-direction cleavedfacet for a laser device according to an embodiment of the presentinvention;

FIG. 4 is a top-view diagram of a laser device according to anembodiment of the present invention;

FIGS. 5 to 12 illustrate a simplified backend processing method of alaser device according to one or more embodiments of the presentinvention;

FIG. 13 is a simplified diagram illustrating a laser device according toone or more examples of the present invention;

FIG. 14 is a simplified diagram illustrating performance of a 300 mWlaser device according to an alternative example of the presentinvention;

FIGS. 15 and 16 are simplified diagrams illustrating performance of asingle-lateral mode blue laser devices with over 21% and 22% [peak] wallplug efficiency (WPE) operating at a wavelength of about 442 nmaccording to an alternative example of the present invention;

FIG. 17 is a simplified diagram illustrating performance of a 550 mWlaser device according to an alternative example of the presentinvention; and

FIG. 18 is a detailed plot of pulsed slope efficiency versus thresholdcurrent for a plurality of blue lasers having different barrierthicknesses ranging from 1.5 nm to 5.0 nm to demonstrate that laserscharacterized with barriers in the 1.5 nm to 2.5 nm range demonstratelower threshold current and higher slope efficiency according toembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, techniques related generally tooptical devices are provided. More particularly, the present inventionprovides a method and device for emitting electromagnetic radiationusing non-polar or semipolar gallium containing substrates such as GaN,AlN, InN, InGaN, AlGaN, and AlInGaN, and others. The invention can beapplied to optical devices, lasers, light emitting diodes, solar cells,photoelectrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors, among otherdevices.

FIG. 1 is a simplified perspective view of a laser device 100 fabricatedon a nonpolar substrate according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize other variations, modifications, and alternatives. Asshown, the optical device includes a gallium nitride substrate member101 having a nonpolar crystalline surface region characterized by anorientation of about −2 degrees to about 2 degrees towards (0001) andless than about 0.5 degrees towards (11-20). In a specific embodiment,the gallium nitride substrate member is a bulk GaN substratecharacterized by having a nonpolar crystalline surface region, but canbe others. In a specific embodiment, the bulk GaN substrate has asurface dislocation density below 10⁵ cm⁻² or 10E5 to 10E7 cm-2. Itshould be noted that homoepitaxial growth on bulk GaN is generallybetter than hetero-epitaxy growth. The nitride crystal or wafer maycomprise Al_(x)In_(y)Ga_(1-x-y)N, where 0≦x, y, x+y≦1. In one specificembodiment, the nitride crystal comprises GaN. In one or moreembodiments, the GaN substrate has threading dislocations, at aconcentration between about 10⁵ cm⁻² and about 10⁸ cm⁻², in a directionthat is substantially orthogonal or oblique with respect to the surface.As a consequence of the orthogonal or oblique orientation of thedislocations, the surface dislocation density is below about 10⁵ cm⁻² orothers such as those ranging from about 10E5-10E8 cm-2.

In a specific embodiment, the device has a laser stripe region formedoverlying a portion of the nonpolar crystalline orientation surfaceregion. In a specific embodiment, the laser stripe region ischaracterized by a cavity orientation is substantially parallel to thec-direction. In a specific embodiment, the laser stripe region has afirst end 107 and a second end 109.

In a preferred embodiment, the device has a first cleaved c-face facetprovided on the first end of the laser stripe region and a secondcleaved c-face facet provided on the second end of the laser striperegion. In one or more embodiments, the first cleaved c-facet issubstantially parallel with the second cleaved c-facet. Mirror surfacesare formed on each of the cleaved surfaces. The first cleaved c-facetcomprises a first mirror surface. In a preferred embodiment, the firstmirror surface is provided by a scribing and breaking process. Thescribing process can use any suitable techniques, such as a diamondscribe or laser scribe or combinations. In a specific embodiment, thefirst mirror surface comprises a reflective coating. In a specificembodiment, deposition of the reflective coating occurs using, forexample, electron beam (ebeam) evaporation, thermal evaporation, RFsputtering, DC sputtering, ECR sputtering, ion beam deposition, IonAssisted Deposition, reactive ion plating, any combinations, and thelike. In still other embodiments, the present method may provide surfacepassivation to the exposed cleaved surface prior to coating. Thereflective coating is selected from silicon dioxide, hafnia, andtitania, tantalum pentoxide, zirconia, including combinations, and thelike. Preferably, the reflective coating is highly reflective andincludes a coating of silicon dioxide and tantalum pentoxide, which hasbeen deposited using electron beam deposition. Depending upon theembodiment, the first mirror surface can also comprise ananti-reflective coating.

Also in a preferred embodiment, the second cleaved c-facet comprises asecond mirror surface. The second mirror surface is provided by ascribing and breaking process according to a specific embodiment.Preferably, the scribing is diamond scribed or laser scribed or thelike. In a specific embodiment, the second mirror surface comprises areflective coating, such as silicon dioxide, hafnia, titania, tantalumpentoxide, zirconia, combinations, and the like. In a specificembodiment, the second mirror surface comprises an anti-reflectivecoating. In a specific embodiment, the coating can be formed usingelectron beam deposition, thermal evaporation, RF sputtering, DCsputtering, ECR sputtering, ion beam deposition, ion assisteddeposition, reactive ion plating, any combinations, and the like. Instill other embodiments, the present method may provide surfacepassivation to the exposed cleaved surface prior to coating.

In a specific embodiment, the laser stripe has a length and width. Thelength ranges from about 50 microns to about 3000 microns. The stripealso has a width ranging from about 0.5 microns to about 50 microns, butcan be other dimensions. In a specific embodiment, the stripe can alsobe about 1 to 20 microns or 1 to 2 microns for a single lateral modelaser device. In a specific embodiment, the width is substantiallyconstant in dimension, although there may be slight variations. Thewidth and length are often formed using a masking and etching process,which are commonly used in the art.

In a specific embodiment, the device is also characterized by aspontaneously emitted light is polarized in substantially perpendicularto the c-direction. That is, the device performs as a laser or the like.In a preferred embodiment, the spontaneously emitted light ischaracterized by a polarization ratio of greater than 0.1 to about 1perpendicular to the c-direction. In a preferred embodiment, thespontaneously emitted light characterized by a wavelength ranging fromabout 400 nanometers to yield a violet emission, a blue emission, agreen emission, and others. In other embodiments, the wavelength rangeis within about 405 nm or slightly more or less. In one or moreembodiments, the light can be emissions ranging from violet 395 to 420nanometers; blue 430 to 470 nm; green 500 to 540 nm; and others, whichmay slightly vary depending upon the application. In a preferredembodiment, the spontaneously emitted light is in the wavelength rangeof 430 nm and greater and is highly polarized with a polarization ratioof greater than 0.4. In a preferred embodiment, the spontaneouspolarization ratio is greater than 0.3 for an emission polarizedperpendicular to the c-direction for a spontaneous emission peakwavelength greater than 430 nm. In a specific embodiment, the emittedlight is characterized by a polarization ratio that is desirable.

FIG. 2 is a detailed cross-sectional view of a laser device 200fabricated on a nonpolar substrate according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art would recognize other variations, modifications, andalternatives. As shown, the laser device includes gallium nitridesubstrate 203, which has an underlying n-type metal back contact region201. In a specific embodiment, the metal back contact region is made ofa suitable material such as those noted below and others.

In a specific embodiment, the device also has an overlying n-typegallium nitride layer 205, an active region 207, and an overlying p-typegallium nitride layer structured as a laser stripe region 211.Additionally, the device also includes an n-side separate confinementhetereostructure (SCH) 206, p-side guiding layer or SCH 208, p-AlGaN EBL209, among other features. In a specific embodiment, the device also hasa p++ type gallium nitride material 213 to form a contact region. In aspecific embodiment, the p++ type contact region has a suitablethickness and may range from about 10 nm 50 nm, or other thicknesses. Ina specific embodiment, the doping level can be higher than the p-typecladding region and/or bulk region. In a specific embodiment, the p++type region has doping concentration ranging from about 10E19 to 10E21Mg/centimeter³, and others. The p++ type region preferably causestunneling between the semiconductor region and overlying metal contactregion. In a specific embodiment, each of these regions is formed usingat least an epitaxial deposition technique of metal organic chemicalvapor deposition (MOCVD), molecular beam epitaxy (MBE), or otherepitaxial growth techniques suitable for GaN growth. In a specificembodiment, the epitaxial layer is a high quality epitaxial layeroverlying the n-type gallium nitride layer. In some embodiments the highquality layer is doped, for example, with Si or O to form n-typematerial, with a dopant concentration between about 10¹⁶ cm⁻³ and 10²⁰cm⁻³.

In a specific embodiment, an n-type Al_(u)In_(v)Ga_(1-u-v)N layer, where0≦u, v, u+v≦1, is deposited on the substrate. In a specific embodiment,the carrier concentration may lie in the range between about 10¹⁶ cm⁻³and 10²⁰ cm⁻³. The deposition may be performed using metalorganicchemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 900 to about 1200degrees Celsius in the presence of a nitrogen-containing gas. As anexample, the carrier can be hydrogen or nitrogen or others. In onespecific embodiment, the susceptor is heated to approximately about 900to about 1100 degrees Celsius under flowing ammonia. A flow of agallium-containing metalorganic precursor, such as trimethylgallium(TMG) or triethylgallium (TEG) is initiated, in a carrier gas, at atotal rate between approximately 1 and 50 standard cubic centimeters perminute (sccm). The carrier gas may comprise hydrogen, helium, nitrogen,or argon. The ratio of the flow rate of the group V precursor (e.g.,ammonia) to that of the group III precursor (trimethylgallium,triethylgallium, trimethylindium, trimethylaluminum) during growth isbetween about 2000 and about 12000. A flow of disilane in a carrier gas,with a total flow rate of between about 0.1 and 10 sccm is initiated.

In a specific embodiment, the laser stripe region is made of the p-typegallium nitride layer 211. In a specific embodiment, the laser stripe isprovided by an etching process selected from dry etching or wet etching.In a preferred embodiment, the etching process is dry, but can beothers. As an example, the dry etching process is an inductively coupledplasma (ICP) process using chlorine bearing species or a reactive ionetching (RIE) process using similar chemistries or combination of ICPand RIE, among other techniques. Again as an example, the chlorinebearing species are commonly derived from chlorine gas or the like. Thedevice also has an overlying dielectric region, which exposes 213contact region, which is preferably a p++ gallium nitride region. In aspecific embodiment, the dielectric region is an oxide such as silicondioxide or silicon nitride, but can be others, such as those describedin more detail throughout the present specification and moreparticularly below. The contact region is coupled to an overlying metallayer 215. The overlying metal layer is a multilayered structurecontaining gold and platinum (Pt/Au) or nickel and gold (Ni/Au), but canbe others. In a specific embodiment, the Ni/Au is formed viaelectro-beam deposition, sputtering, or any like techniques. Thethickness includes nickel material ranging in thickness from about 50 toabout 100 nm and gold material ranging in thickness from about 1000Angstroms to about 1-3 microns, and others.

In a preferred embodiment, the dielectric region can be made using asuitable technique. As an example, the technique may include reactivelysputter of SiO2 using an undoped polysilicon target (99.999% purity)with O2 and Ar. In a specific embodiment, the technique uses RFmagnetron sputter cathodes configured for static deposition; sputtertarget; throw distance; pressure: 1-5 mT or about 2.5 mT, power: 300 to400 W; flows: 2-3.-9 sccm O2, 20-50 sccm, Ar, deposition thickness:1000-2500 A, and may include other variations. In a specific embodiment,deposition may occur using non-absorbing, nonconductive films, e.g.,Al2O3, Ta2O5, SiO2, Ta2O5, ZrO2, TiO2, HfO2, NbO2. Depending upon theembodiment, the dielectric region may be thinner, thicker, or the like.In other embodiments, the dielectric region can also include multilayercoatings, e.g., 1000 A of SiO2 capped with 500 A of Al2O3. Depositiontechniques can include, among others, ebeam evaporation, thermalevaporation, RF Sputter, DC Sputter, ECR Sputter, Ion Beam Deposition,Ion Assisted Deposition, reactive ion plating, combinations, and thelike.

In a specific embodiment, the laser device has active region 207. Theactive region can include one to twenty quantum well regions accordingto one or more embodiments. As an example following deposition of then-type Al_(u)In_(v)Ga_(1-u-v)N layer for a predetermined period of time,so as to achieve a predetermined thickness, an active layer isdeposited. The active layer may comprise a single quantum well or amultiple quantum well, with 1-20 quantum wells. Preferably, the activelayer may include about 3-7 quantum wells or more preferably 4-6 quantumwells or others. The quantum wells may comprise InGaN wells and GaN orInGaN barrier layers. In other embodiments, the well layers and barrierlayers comprise Al_(w)In_(x)Ga_(1-w-x)N and Al_(y)In_(z)Ga_(1-y-z)N,respectively, where 0≦w, x, y, z, w+x, y+z≦1, where w<u, y and/or x>v, zso that the bandgap of the well layer(s) is less than that of thebarrier layer(s) and the n-type layer. The well layers and barrierlayers may each have a thickness between about 1 nm and about 40 nm. Ina preferred embodiment, each of the thicknesses is preferably 1-8 nm. Ina specific embodiment, each well region may have a thickness of about 4nm to 6 nm and each barrier region may have a thickness of about 1 nm toabout 5 nm, among others. In alternative specific embodiment, each wellregion may have a thickness of about 4 nm to 6 nm and each barrierregion may have a thickness of about 1 nm to about 3 nm, among others.In alternative specific embodiment, each well region may have athickness of about 2.5 nm to 4.5 nm and each barrier region may have athickness of about 2 nm to about 4 nm, among others. In anotherembodiment, the active layer comprises a double heterostructure, with anInGaN or Al_(w)In_(x)Ga_(1-w-x) N layer about 10 nm to 100 nm thicksurrounded by GaN or Al_(y)In_(z)Ga_(1-y-z)N layers, where w<u, y and/orx>v, z. The composition and structure of the active layer are chosen toprovide light emission at a preselected wavelength. The active layer maybe left undoped (or unintentionally doped) or may be doped n-type orp-type.

In a specific embodiment, the active region can also include an electronblocking region, and a separate confinement heterostructure. In aspecific embodiment, the separate confinement heterostructure (SCH) caninclude AlInGaN or preferably InGaN, but can be other materials. The SCHis generally comprised of material with an intermediate index betweenthe cladding layers and the active layers to improve confinement of theoptical mode within the active region of the laser device according to aspecific embodiment. In one or more embodiments, the SCH layers have adesirable thickness, impurity, and configuration above and below theactive region to confine the optical mode. Depending upon theembodiment, the upper and lower SCH can be configured differently or thesame. The electron blocking region can be on either side or both sidesof the SCH positioned above the active region according to a specificembodiment. In a preferred embodiment, the lower SCH can range fromabout 10 nm to about 150 nm, and preferably about 40 to 120. The lowerSCH is preferably InGaN having with about 2% to about 10% indium byatomic percent according to a specific embodiment. In a preferredembodiment the upper SCH region thickness ranges from about 10 to 150nm, and preferably about 10 nm to 50 nm. The upper SCH is preferably GaNor InGaN having about 0% to about 5% indium by atomic percent accordingto a specific embodiment. In the case that that there is no indium inthis upper layer, the layer can be referred to as an p-side guidinglayer that is comprised of GaN.

In some embodiments, an electron blocking layer is preferably deposited.In a specific embodiment, the electron blocking layer comprises agallium and nitrogen containing material including magnesium 10E16 cm-3to about 10E22 cm-3. The electron-blocking layer may compriseAl_(s)In_(t)Ga_(1-s-t)N, where 0≦s, t, s+t≦1, with a higher bandgap thanthe active layer, and may be doped p-type. In one specific embodiment,the electron blocking layer comprises AlGaN with an Al compositionranging from 10 to 20%. In another specific embodiment, the electronblocking layer comprises AlGaN with an Al composition ranging from 3 to10%. In another embodiment, the electron blocking layer may not containAl. In another embodiment, the electron blocking layer comprises anAlGaN/GaN super-lattice structure, comprising alternating layers ofAlGaN and GaN, each with a thickness between about 0.2 nm and about 5nm.

In some embodiments, there may not be an electron blocking layer. In aspecific embodiment, the AlGaN blocking layer is replaced by a GaN layerdoped with magnesium from about 10E16 cm-3 to about 10E22 cm-3.

In a specific embodiment, the present invention provides a laser deviceand related methods using thin barrier materials to achieve improvedperformance. In a specific embodiment for a nonpolar blue laser withmulti-quantum well (MQW) active regions comprised of 4-7 QWs withthicknesses in the 4 to 6 nm range, barrier thicknesses in the 1.5 nm to2.5 nm range provide the lowest threshold current, highest slopeefficiency, and lower forward voltage. Blue laser diodes employing suchMQW active regions with 3 or more, or 5 or more QWs fabricated onconventional c-plane GaN would be impractical due to the high strainaccumulation, which would likely lead to the onset of defects.

By reducing the barrier thickness to the present ultra-thin 1.5 to 2.5nm regime, the outer quantum wells within the active region are pushedin towards the peak of the optical mode. In other embodiments, theultra-thin barrier can be 1.0 nm and less, although there can be somevariations. In other embodiments, the ultra-thin barrier can be 2.5 nmand less or 2.0 nm and less. This results in higher optical overlap ofthe electric field and the quantum wells within the laser. Since themodal gain of a laser is given by the product of the material gain andthe optical confinement, this increase in the optical confinementresults in increased modal gain. Increased gain reduces the thresholdcurrent density, and hence reduces the threshold current in a laser witha given cavity dimension.

Thin barriers can further increase the laser performance by againincreasing the modal gain and by reducing absorption losses in thequantum wells by promoting a more uniform carrier distributionthroughout the quantum wells according to a specific embodiment. Theheavy effective mass of holes typically limits carrier transport inmulti-quantum well InGaN-based devices. With a reduced total transportlength from the p-side of the active region where holes are injected tothe lower quantum wells towards the n-side, holes are more readily ableto travel to the lowest quantum wells before recombining with anelectron. Such thin barriers increase the probability for holes totunnel through the barriers such that they do not need to overcome thepotential energy of the hole/barrier hetereointerface. This againpromotes more uniform carrier filling of the quantum wells. This moreuniform carrier distribution profile assures that no wells are leftun-pumped such that they are absorbing or lossy to the optical mode. Thehigher loss associated with insufficiently pumped wells leads to anincreased threshold current and a decreased slope efficiency. Further,the carrier uniformity prevents the case where a majority of thecarriers are recombining in only some of the quantum wells such that thecarrier concentration would become very high in those wells and the gainwould saturate. A uniform carrier distribution guarantees that eachquantum well is kept as far from gain saturation as possible for a givenlaser injection current.

A reduced transport length and a higher probability for carriertunneling through the barriers could also reduce the forward voltage ofthe laser diode. Again, there can be other variations, modifications,and alternatives. As an alternative example for the present semipolargreen laser operating in the 510 to 530 nm range, thin barriers can alsobe employed. In one embodiment for a green laser structure, 4 to 5quantum wells with thicknesses that range from 3 nm to 4.5 nm andbarriers that range in thickness from 2 nm to 4.5 nm can be employed.

As noted, the p-type gallium nitride structure, which can be a p-typedoped Al_(q)In_(r)Ga_(1-q-r)N, where 0≦q, r, q+r≦1, layer is depositedabove the active layer. The p-type layer may be doped with Mg, to alevel between about 10¹⁶ cm⁻³ and 10²² cm⁻³, and may have a thicknessbetween about 5 nm and about 1000 nm. The outermost 1-50 nm of thep-type layer may be doped more heavily than the rest of the layer, so asto enable an improved electrical contact. In a specific embodiment, thelaser stripe is provided by an etching process selected from dry etchingor wet etching. In a preferred embodiment, the etching process is dry,but can be others. The device also has an overlying dielectric region,which exposes 213 contact region. In a specific embodiment, thedielectric region is an oxide such as silicon dioxide.

In a specific embodiment, the metal contact is made of suitablematerial. The reflective electrical contact may comprise at least one ofsilver, gold, aluminum, nickel, platinum, rhodium, palladium, chromium,or the like. The electrical contact may be deposited by thermalevaporation, electron beam evaporation, electroplating, sputtering, oranother suitable technique. In a preferred embodiment, the electricalcontact serves as a p-type electrode for the optical device. In anotherembodiment, the electrical contact serves as an n-type electrode for theoptical device.

In a specific embodiment, a ridge waveguide is fabricated using acertain deposition, masking, and etching processes. In a specificembodiment, the mask is comprised of photoresist (PR) or dielectric orany combination of both and/or different types of them. The ridge maskis 1 to 2.5 microns wide for single lateral mode applications or 2.5 to30 um wide for multimode applications. The ridge waveguide is etched byion-coupled plasma (ICP), reactive ion etching (RIE), or other method.The etched surface is 25-250 nm above the active region. A dielectricpassivation layer is then blanket deposited by any number of commonlyused methods in the art, such as sputter, e-beam, PECVD, or othermethods. This passivation layer can include SiO2, Si3N4, Ta2O5, orothers. The thickness of this layer is 80-400 nm thick. An ultrasonicprocess is used to remove the etch mask which is covered with thedielectric. This exposes the p-GaN contact layer. P-contact metal isdeposited by e-beam, sputter, or other deposition technique using a PRmask to define the 2D geometry. The contact layer can be Ni/Au butothers can be Pt/Au or Pd/Au.

FIG. 3 is a cross-sectional view photograph of a c-direction cleavedfacet for a laser device according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize other variations, modifications, and alternatives. Asshown, the c-direction cleaved facet is smooth and provides a suitablemirror surface.

FIG. 4 is a top-view diagram of a laser device according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims herein. One ofordinary skill in the art would recognize other variations,modifications, and alternatives. As shown, the laser stripe isconfigured in the c-direction, which has a projection normal to thec-direction. As shown, the top-view of the gallium nitride substrate isof a slight mis-cut or off-cut surface region orientation according to aspecific embodiment.

A method of processing a laser device according to one or moreembodiments may be outline as follows, see also FIG. 5:

1. Start;

2. Provide processed substrate including laser devices with ridges;

3. Thin substrate from backside;

4. Form backside n-contact;

5. Scribe pattern for separation of the laser devices configured in barstructures;

6. Break scribed pattern to form a plurality of bar structures;

7. Stack bar structures;

8. Coat bar structures;

9. Singulate bar structures into individual dies having laser device;and

10. Perform other steps as desired.

The above sequence of steps is used to form individual laser devices ona die from a substrate structure according to one or more embodiments ofthe present invention. In one or more preferred embodiments, the methodincludes cleaved facets substantially parallel to each other and facingeach other in a ridge laser device configured on a non-polar galliumnitride substrate material. Depending upon the embodiment, one or moreof these steps can be combined, or removed, or other steps may be addedwithout departing from the scope of the claims herein. One of ordinaryskill in the art would recognize other variations, modifications, andalternatives.

FIG. 6 is a simplified illustration of a substrate thinning processaccording to an embodiment of the present invention. This diagram ismerely an illustration and should not unduly limit the scope of theclaims herein. One of ordinary skill in the art would recognize othervariations, modifications, and alternatives. In a specific embodiment,the method begins with a gallium nitride substrate material includinglaser devices and preferably ridge laser devices, but can be others. Thesubstrate has been subjected to frontside processing according to aspecific embodiment. After frontside processing has been completed, oneor more of the GaN substrates are mounted onto a sapphire carrier waferor other suitable member. As an example, the method uses Crystalbond509, which is a conventional mounting thermoplastic. The thermoplasticcan be dissolved in acetone or other suitable solvent.

In a specific embodiment, the carrier wafer is mounted to a lapping jig.An example of such lapping jig is made by Logitech Ltd. of the UnitedKingdom, or other vendor. The lapping jig helps maintain planarity ofthe substrates during the lapping process according to a specificembodiment. As an example, the starting thickness of the substrates are˜325 um+/−20 um, but can be others, e.g., 250 to about 500 um. In aspecific embodiment, the method laps or thins the substrates down to60-70-80 um thickness, but can also be thinner or slightly thicker. In apreferred embodiment, the lapping jig is configured with a lappingplate, which is often made of a suitable material such as cast ironconfigured with a flatness of less than 5 um, but can be others.Preferably, the method uses a lapping slurry that is 1 part siliconcarbide (SiC) and 10 parts water, but can also be other variations. In aspecific embodiment, the SiC grit is about 5 um or 9 micron and othersin dimension. In one or more embodiments, the lapping plate speed issuitable at about 10 revolutions per minute. Additionally, the methodcan adjust the lapping jig's down pressure to achieve a desired lappingrate, such as 2-3 um/min or greater or slightly less according to one ormore embodiments.

In a preferred embodiment, the present method uses a suitable lappingprocess. Such process includes use of a Logitech LP50 lapping/polishingsystem using a suitable slurry mixture. The slurry may include a SiCslurry such as 9 um SiC slurry (from Logitech), among others. The slurrymay be mixed with a SiC to water ratio such as 1:10 SiC:H2O, or others,e.g., 1-3:8-12. In a preferred embodiment, the lapping occurs at about 5to about 50 rpm and is preferably about 10 rpm, which achieves a removalrate of about 1-5 um/min removal rate. Lapping occurs until thethickness of the substrate is about 80 um or 75 um and less. In othervariations, grin ding may be used to replace or supplement lapping.Other variations include other lapping materials and grits, such asAl2O3, diamond, boron nitride, combinations, and others. Grit size canalso range from about 1 um, 3 um, 5 um, 15 um, combinations, and others.Lapping is often followed by polishing, which will be described in moredetail below.

In a specific embodiment, the present method uses a suitable polishingprocess. In a specific embodiment, polishing occurs using the LogitechLP50 lapping/polishing system. In a specific embodiment, diamondpolishing material includes a 1 um diamond suspension (from Eminess)configured on a polish pad, e.g., SUBA IV, 40-80 rpm or 70 rpm, but canbe others. The polishing occurs to achieve a 3-5 um/hr removal rate andremoves about 5 to 10 microns of substrate material, which leaves thesubstrate thickness at about 65 um. In other embodiments, polishing maybe optional.

In a specific embodiment, the present method includes a lapping processthat may produce subsurface damage in the GaN material to causegeneration of mid level traps or the like. The midlevel traps may leadto contacts having a Schottky characteristic. Accordingly, the presentmethod includes one or more polishing processes such that ˜10 um ofmaterial having the damage is removed according to a specificembodiment. As an example, the method uses a Politex™ polishing pad ofRohm and Haas, but can be others, that is glued onto a stainless steelplate. A polishing solution is Ultrasol300K manufactured by EminessTechnologies, but can be others. The Ultra-Sol 300K is a high-puritycolloidal silica slurry with a specially designed alkaline dispersion.It contains 70 nm colloidal silica and has a pH of 10.6 in a specificembodiment. The solids content is 30% (by weight), but can range fromabout 20 to 50% by weight. In a specific embodiment, the lapping platespeed is 70 rpm (or range from about 40 to 100 rpm) and the full weightof the lapping jig is applied. In a preferred embodiment, the methodincludes a polishing rate of about ˜2 um/hour, but can be others, whichare higher or lower.

In other embodiments, the present invention provides a method forachieving high quality n-type contacts for m-plane GaN substratematerial. In a specific embodiment, the method provides contacts thatare rough to achieve suitable ohmic contact. In a specific embodiment,the roughness causes exposure of other crystal planes, which lead togood contacts. In a preferred embodiment, the present method includes alapped surface, which is rough in texture to expose more than one ormultiple different crystal planes. In other embodiments, lapping may befollowed by etching such as dry etching with (Cl2/BCl3)/SiCl4/Cl2 basedchemistries and/or wet etching. In a specific embodiment, etchingremoves the subsurface damage, however, it is likely not to planarizethe surface like polishing.

FIG. 7 is a simplified diagram illustrating a backside n-contact methodaccording to one or more embodiments. This diagram is merely anillustration and should not unduly limit the scope of the claims herein.One of ordinary skill in the art would recognize other variations,modifications, and alternatives. After the thinning process is complete,the method forms n-contacts on the backside of the substrates accordingto one or more embodiments. At this point, the thinned substrates arestill mounted to and maintained on the sapphire wafer. In a preferredembodiment, the thinned substrates are “batch process” for efficiencyand handling. In a specific embodiment, the method using batchprocessing helps prevent any damage associated with handling very thin(60-80 um) substrates.

In a specific embodiment, the backside contact regions are formed usinglaser irradiation as a pre-treatment before contact formation. In aspecific embodiment, the laser irradiation can be performed using ascribing process by way of laser irradiation. An example is described inU.S. Ser. No. 61/345,561, which is commonly assigned, and herebyincorporated by reference.

As an example, the backside contact includes about 300 Å Al/3000 Å Au orother suitable materials. In a specific embodiment, the contact is astack of metals that are deposited by e-beam evaporation or othersuitable techniques. In a specific embodiment, the contacts can includealuminum/nickel/gold materials having respective thicknesses of, forexample, 300/1000/3000 Angstroms or Ti/Pt/Au materials having respectivethicknesses of, for example, 200/400/3000 Angstroms, or others. In apreferred embodiment and prior to the metal stack deposition, the methodincludes use of a wet etch such as a hydrofluoric acid or hydrochloricwet etch to remove any oxides on the surface. In a specific embodiment,the metal stack is preferably not annealed or subjected to hightemperature processing after its formation. In other embodiments, themetal stack may be annealed directly or indirectly via radiation,conduction, convection, or combinations thereof.

FIG. 8 is a simplified diagram illustrating a scribe and break operationaccording to one or more embodiments. This diagram is merely anillustration and should not unduly limit the scope of the claims herein.One of ordinary skill in the art would recognize other variations,modifications, and alternatives. After the n-contact is formed, thesubstrates are demounted from the sapphire carrier wafer and cleaned inacetone and isopropyl alcohol according to a specific embodiment. Thesubstrates are then mounted onto vinyl tape for the scribe and breakprocess depending upon the embodiment. In a preferred embodiment, thevinyl tape is non-tacky or other suitable configuration. In a preferredembodiment, the tape does not leave any residue on the laser bars, whichare substantially free from such residues, which are often polymeric innature or particulates. In other embodiments, there may be some residualmaterial from the tape that is preferably removed.

In a specific embodiment, the present method performs a cleaning processto remove residual material from the substrate. After demounting thesubstrate from the tape, residue is often leftover from wax or otheradhesive material from the tape. In a specific embodiment, the methodremoves the residue using at least a de-scum process. The de-scumprocess can include an oxygen plasma from an inductively coupled plasmausing an oxygen species, e.g., O2. An example of such process uses anOxford ICP 180, a vacuum pressure ranging in the millitorr range, suchas 20 mT, a flow rate of oxygen from about 10 sccm to about 100 sccm,and preferably about 50 sccm of O₂ gas. The ICP uses RF power rangingfrom about 50 W to about 300 W ICP for a suitable amount of time andpreferably about 10 minutes to remove the wax material. Other plasmaprocesses such as reactive ion etching, barrel ashing, down streamashing, and others may also be used.

Next, the method includes one or more scribing processes. In a specificembodiment, the method includes subjecting the substrates to a laser forpattern formation. In a preferred embodiment, the pattern is configuredfor the formation of a pair of facets for one or more ridge lasers. In apreferred embodiment, the pair of facets face each other and are inparallel alignment with each other. In a preferred embodiment, themethod uses a UV (355 nm) laser to scribe the laser bars. In a specificembodiment, the laser is configured on a system, which allows foraccurate scribe lines configured in one or more different patterns andprofiles. In one or more embodiments, the scribing can be performed onthe backside, frontside, or both depending upon the application.

In a specific embodiment, the method uses backside scribing or the like.With backside scribing, the method preferably forms a continuous linescribe that is perpendicular to the laser bars on the backside of theGaN substrate. In a specific embodiment, the scribe is generally 15-20um deep or other suitable depth. Preferably, backside scribing can beadvantageous. That is, the scribe process does not depend on the pitchof the laser bars or other like pattern. Accordingly, backside scribingcan lead to a higher density of laser bars on each substrate accordingto a preferred embodiment. In a specific embodiment, backside scribing,however, may lead to residue from the tape on one or more of the facets.In a specific embodiment, backside scribe often requires that thesubstrates face down on the tape. With front-side scribing, the backsideof the substrate is in contact with the tape. In one or moreembodiments, front side scribing may be used for die separation.

In a specific embodiment, the present method performs a cleaning processto remove residual material from the substrate. After demounting thesubstrate from the tape, residue is often leftover from wax or otheradhesive material from the tape. In a specific embodiment, the methodremoves the residue using at least a de-scum process. The de-scumprocess can include an oxygen plasma from an inductively coupled plasmausing an oxygen species, e.g., O2. An example of such process uses anOxford ICP 180, a vacuum pressure ranging in the millitorr range, suchas 20 mT, a flow rate of oxygen from about 10 sccm to about 100 sccm,and preferably about 50 sccm of O₂ gas. The ICP uses RF power rangingfrom about 50 W to about 300 W ICP for a suitable time or preferablyabout 10 minutes to remove the wax material. Other plasma processes suchas reactive ion etching, barrel ashing, down stream ashing, and othersmay also be used.

In a preferred embodiment, the present method uses frontside scribing,which facilitates formation of clean facets. In a specific embodiment,the frontside scribing process is preferably used. In a specificembodiment, the method includes a scribe pattern to produce straightcleaves with minimal facet roughness or other imperfections. Furtherdetails of scribing are provided below.

Scribe Pattern: The pitch of the laser mask can be about 200 um, but canbe others. In the case of a 200 um pitch, the method uses a 170 umscribe with a 30 um dash. In a preferred embodiment, the scribe lengthis maximized or increased while maintaining the heat affected zone ofthe laser away from the laser ridge, which is sensitive to heat.

Scribe Profile: A saw tooth profile generally produces minimal facetroughness. It is believed that the saw tooth profile shape creates avery high stress concentration in the material, which causes the cleaveto propogate much easier and/or more efficiently. In a specificembodiment, the profile may be a shallow scribe, which produces arecessed region. The shallow scribe ranges from about 3 to 10 micronsand is preferably about 4 to 7 microns depending upon the specificembodiment.

In a specific embodiment, the present method uses an Opto Laser Scriberconfigured with a 355 nm laser or other suitable source. The laseroutputs selected pulses to form a desirable scribe characterized with askip. The scribe generally has a constant depth of ˜5-10 um but can beothers. The scriber also has a power of 100 mW to about 300 mW or othersuitable power and has a beam moving at about 25 to about 100 mm/s, butcan be slightly more or less, or other speeds. In a specific embodiment,the method also performs a slag removal process to remove the slag fromthe laser scribe using wet chemistry, e.g., 0.5-1.5:2.5-3.5 or 1:3,HNO₃:HCl, but can be others. The slag removal process improves the laserand its cleanliness in a preferred embodiment. In other embodiments, themethod can use different laser configurations (e.g., differentwavelength, different pulse frequency), a mechanical scribing process(e.g, diamond scribing), or deep etching using wet and/or drytechniques.

In a specific embodiment, the present method provides for a scribesuitable for fabrication of the present laser devices. As an example,FIG. 9 illustrates cross-sections of substrate materials associated with(1) a backside scribe process; and (2) a frontside scribe process.

Referring now to FIG. 10, the method includes a breaking process to forma plurality of bar structures. This diagram is merely an illustrationand should not unduly limit the scope of the claims herein. One ofordinary skill in the art would recognize other variations,modifications, and alternatives. After the GaN substrates are scribed,the method uses a breaker to cleave the substrates into bars. In aspecific embodiment, the breaker has a metal support that has a gapspacing of 900 um for 600 micron long laser cavities. The substrate ispositioned over the support so that the scribe line is in the centered.A suitably sharp ceramic blade, then applies pressure directly on thescribe line causing the substrate to cleave along the scribe line.

FIG. 11 is a simplified diagram illustrating a stacking and coatingprocess according to one or more embodiments. Again, this diagram ismerely an illustration and should not unduly limit the scope of theclaims herein. One of ordinary skill in the art would recognize othervariations, modifications, and alternatives. After cleaving, the barsare stacked in a fixture that allows for coating the front facet andback facet, which are in parallel alignment with each other and facingeach other. The front facet coating films can be selected from anysuitable low reflectance design (AR design). The AR design includes aquarterwave coating of Al₂O₃ capped with a thin layer of HfO₂ accordingto a specific embodiment. The Al₂O₃ coating is a robust dielectric, andHfO₂ is dense, which helps environmentally passivate and tune thereflectance of the front facet. These coating films are preferablydeposited by e beam evaporation. Other examples include thermalevaporation, RF sputtering, DC sputtering, ECR sputtering, ion beamdeposition, Ion Assisted Deposition, reactive ion plating, anycombinations, and the like. In still other embodiments, the presentmethod may provide surface passivation to the exposed cleaved surfaceprior to coating. In a specific embodiment, the back facet is coatedwith a high reflectance HR design. The HR design includes severalquarterwave pairs of SiO₂/HfO₂. In a preferred embodiment, the HR designincludes several quarterwave layer pairs of SiO2/Ta2O5 or other suitablematerials. In a specific embodiment, roughly 6-7 pairs may be used toachieve a reflectance over 99%.

In a preferred embodiment, the method uses a suitable deposition systemconfigured for deposition of each of the facets without breaking vacuum.The deposition system includes a dome structure with sufficient heightand spatial volume. The system allows for the plurality of barsconfigured in a fixture to be flipped from one side to another side andto expose the back facet and the front facet according to a specificembodiment. In a preferred embodiment, the method allows for firstdeposition of the back facet, reconfiguring the bar fixture to exposethe front facet, and second deposition of the front facet withoutbreaking vacuum. In a preferred embodiment, the method allows fordeposition of one or more films on front and back without breakingvacuum to save time and improve efficiency. Other embodiments can breakvacuum.

FIG. 12 illustrates a method directed to singulate bars into a pluralityof die according to a specific embodiment. This diagram is merely anillustration and should not unduly limit the scope of the claims herein.One of ordinary skill in the art would recognize other variations,modifications, and alternatives. After the facets of the bars have beencoated, the method includes testing the laser devices in bar form priorto die singulation. In a specific embodiment, the method singulates thebars by performing a scribe and break process (similar to the facetcleave). Preferably, the method forms a shallow continuous line scribeon the top side of the laser bar according to a specific embodiment. Thewidth of each die is about 200 um, which may reduce the support gap to300 um or so. After the bars have been cleaved into individual die, thetape is expanded and each of the die is picked off of the tape. Next,the method performs a packing operation for each of the die according toone or more embodiments.

EXAMPLES

FIG. 13 is a simplified diagram illustrating a laser device according toone or more examples of the present invention. This diagram is merely anillustration and should not unduly limit the scope of the claims herein.One of ordinary skill in the art would recognize other variations,modifications, and alternatives. In this example, the optical deviceincludes a gallium nitride substrate member having a nonpolarcrystalline surface region characterized by an orientation of about +/−1degree towards (0001) and less than about 0.3 degrees towards (11-20).The bulk GaN substrate has a surface dislocation density below 1E5 to1E7 cm-2 or about 1E6 cm⁻² and a surface roughness of less than 0.2 nm.

The device has a laser stripe region formed overlying a portion of thenonpolar crystalline orientation surface region. The laser stripe regionis characterized by a cavity orientation is substantially parallel tothe c-direction and has a first end and a second end. The device has afirst cleaved c-face facet provided on the first end of the laser striperegion and a second cleaved c-face facet provided on the second end ofthe laser stripe region. The first cleaved c-facet is substantiallyparallel with the second cleaved c-facet. Mirror surfaces are formed oneach of the cleaved surfaces. The first cleaved c-facet comprises afirst mirror surface. The first mirror surface is provided by a scribingand breaking process such as the one described herein. The first mirrorsurface comprises a reflective coating, which is alumina and hafnia. Ina specific embodiment, the coating may include combinations ofSiO2/Ta2O5, among other materials, and the like. The second cleavedc-facet comprises a second mirror surface. The second mirror surface isprovided by a scribing and breaking process such as the one describedherein. The second mirror surface comprises a reflective coating, suchas silicon dioxide and hafnia. In a specific embodiment, the laserstripe has a length and width. The length is 400-1000 μm and the widthis 1-1.4-4 μm. The width is substantially constant in dimension.

In a specific embodiment, the facets are configured in a desirablemanner. That is, one of the facets is substantially free from coatingand is generally exposed GaN material having a reflectance ˜18.4% ormore generally from about 10% to about 24%, but can be others. In aspecific embodiment, the other facet is coated with a reflectivematerial. In a specific embodiment, the reflective material may be λ/2coatings of non-absorbing film materials to maintain the same or similarreflectance. Examples of materials include, among others, Al2O3, Ta2O5,SiO2, Ta2O5, ZrO2, TiO2, HfO2, NbO2, or others. In other embodiments,multilayer coatings using combinations of the above materials achievethe same reflectance. In still other embodiments, the coatings includesingle layer coatings with varying reflectances, multilayer coatingswith varying reflectances, or others. In alternative embodiments,coatings may be deposited using similar or different processes and/ortools. As an example, such processes include e-beam evaporation, thermalevaporation, RF sputtering, DC sputtering, ECR sputtering, ion beamdeposition, Ion Assisted Deposition, reactive ion plating, anycombinations, and the like. In still other embodiments, the presentmethod may provide surface passivation to the exposed cleaved surfaceprior to coating.

As shown in the accompanying Figures, the device is also characterizedby a spontaneously emitted light is polarized in substantiallyperpendicular to the c-direction. That is, the device performs as alaser. The spontaneously emitted light is characterized by apolarization ratio perpendicular to the c-direction. As also shown isthe spontaneously emitted light characterized by a wavelength of about405 nanometers to yield blue-violet emission. Other parameters included:

Wavelength: 395 to 415 nm

Power_(CW)>350 mW;

I_(th)<35 mA;

Slope efficiency>1.0 W/A; and

Packaged on TO-56 Header.

As shown, the graph illustrates a power and current relationship for thesubject laser device at about 25 Degrees Celsius. Additionally, thewavelength is indicated at about 405 nanometers for the subject laserdevice. In a preferred embodiment, the present device uses thin barrierregions configured in the active region, which has been describedthroughout the present specification and more particularly below.

FIG. 14 is a simplified diagram illustrating performance of a 300 mWsingle-lateral mode blue laser device operating at a wavelength of 446nm according to an alternative example of the present invention. Thisdiagram is merely an illustration and should not unduly limit the scopeof the claims herein. One of ordinary skill in the art would recognizeother variations, modifications, and alternatives. As shown arecontinuous wave (CW) optical output power plotted against input currentand voltage along with a plot of optical intensity plotted againstwavelength. The light power output plotted against input current andvoltage provides an efficiency of 17.5% at 145 mW for the 300 mW CW bluelaser device. The current and voltage thresholds are also shown. In apreferred embodiment, the present device uses thin barrier regionsconfigured in the active region, which has been described throughout thepresent specification and more particularly below. The laser device issingle mode and has been fabricated using the process and structuresdescribed herein.

Wavelength: 440 to 470 nm

Power_(CW)>300 mW;

I_(th)<40 mA;

Slope efficiency>1.0 W/A; and

Packaged on TO-56 or TO-38 Header.

FIGS. 15 and 16 are simplified diagrams illustrating performance of asingle-lateral mode blue laser devices with over 21% [peak] wall plugefficiency (WPE) operating at a wavelength of about 442 nm according toan alternative example of the present invention. These diagrams aremerely an illustration and should not unduly limit the scope of theclaims herein. One of ordinary skill in the art would recognize othervariations, modifications, and alternatives. As shown in each of theFigures are continuous wave (CW) optical output power plotted againstinput current and voltage along with a plot of WPE versus input currentwith optical intensity plotted against wavelength in the inset. Amaximum WPE is known as the peak WPE, although there may be otherdefinitions. As seen in the plot of WPE versus current, the efficiencyclimbs over 20% at around 80 mA of input current, which translates toaround 80 mW of output power. The single-lateral-mode blue laser devicein FIG. 15 achieves a peak WPE of 21% at an output power of about 130 mWin a specific embodiment. The single-lateral-mode blue laser device inFIG. 14 achieves a peak WPE of 22.7% at an output power of about 170 mWaccording to a specific embodiment. Such WPE values from single lateralmode blue lasers represent state-of-the-art performance. The current andvoltage thresholds are also shown. The laser device is single mode andhas been fabricated using the process and structures described herein.

FIG. 17 is a simplified diagram illustrating performance of a CW 550 mWsingle lateral mode blue laser device according to an alternativeexample of the present invention. This diagram is merely an illustrationand should not unduly limit the scope of the claims herein. One ofordinary skill in the art would recognize other variations,modifications, and alternatives. As shown are optical output powerplotted against input current for a 550 mW CW laser device. The lightpower output plotted against current input provides an efficiency of16.7% at 220 mW for the single lateral mode CW blue laser device. Thedevice has a threshold current of 35 mA, a threshold voltage of 4.1 V,and outputs over 500 mW with about 500 mA of input current. Such outputpowers in the 500 mW range represents state-of-the-art performance fromsingle lateral mode blue laser device. The laser has been fabricatedusing the process and structures described herein.

Referring now to FIG. 18 in a specific embodiment, the present inventionprovides a laser device and related methods using thin barrier materialsto achieve improved performance. As background, we learned thatconventional laser diodes fabricated on c-plane GaN typically employbarrier thicknesses in the 6 nm to 12 nm and greater range. We havediscovered that the performance of laser diodes fabricated on nonpolarand semipolar substrates can be improved by implementing ultra thinbarriers according to the present embodiment, as further described byillustration in FIG. 18. For the present nonpolar blue laser withmulti-quantum well (MQW) active regions comprised of 4-7 QWs withthicknesses in the 4 to 6 nm range, we have found that barrierthicknesses in the 1.5 nm to 2.5 nm range provide the lowest thresholdcurrent, highest slope efficiency, and lower forward voltage accordingto a preferred embodiment. Blue laser diodes employing such MQW activeregions with 3 or more, or 5 or more QWs fabricated on conventionalc-plane GaN would be impractical due to the high strain accumulation,which would likely lead to the onset of defects, as noted.

By reducing the barrier thickness to this ultra-thin 1.5 to 2.5 nmregime, the outer quantum wells within the active region are pushed intowards the peak of the optical mode, as also explained herein. Thisresults in higher optical overlap of the electric field and the quantumwells within the laser. Since the modal gain of a laser is given by theproduct of the material gain and the optical confinement, this increasein the optical confinement results in increased modal gain. Increasedgain reduces the threshold current density, and hence reduces thethreshold current in a laser with a given cavity dimension.

Thin barriers can further increase the laser performance by againincreasing the modal gain and by reducing absorption losses in thequantum wells by promoting a more uniform carrier distributionthroughout the quantum wells according to a specific embodiment. Theheavy effective mass of holes typically limits carrier transport inmulti-quantum well InGaN-based devices. With a reduced total transportlength from the p-side of the active region where holes are injected tothe lower quantum wells towards the n-side, holes are more readily ableto travel to the lowest quantum wells before recombining with anelectron. Such thin barriers increase the probability for holes totunnel through the barriers such that they do not need to overcome thepotential energy of the hole/barrier hetereointerface. This againpromotes more uniform carrier filling of the quantum wells. This moreuniform carrier distribution profile assures that no wells are leftun-pumped such that they are absorbing or lossy to the optical mode. Thehigher loss associated with insufficiently pumped wells leads to anincreased threshold current and a decreased slope efficiency. Further,the carrier uniformity prevents the case where a majority of thecarriers are recombining in only some of the quantum wells such that thecarrier concentration would become very high in those wells and the gainwould saturate. A uniform carrier distribution guarantees that eachquantum well is kept as far from gain saturation as possible for a givenlaser injection current.

A reduced transport length and a higher probability for carriertunneling through the barriers could also reduce the forward voltage ofthe laser diode. Again, there can be other variations, modifications,and alternatives. As an alternative example for the present semipolargreen laser operating in the 510 to 530 nm range, thin barriers can alsobe employed. In one embodiment for a green laser structure, 4 to 5quantum wells with thicknesses that range from 3 nm to 4.5 nm andbarriers that range in thickness from 2 nm to 4.5 nm can be employed.

In other embodiments, the present invention includes a device and methodconfigured on other gallium and nitrogen containing substrateorientations. In a specific embodiment, the gallium and nitrogencontaining substrate is configured on a family of planes including a{20-21} crystal orientation. In a specific embodiment, {20-21} is 14.9degrees off of the m-plane towards the c-plane (0001). As an example,the miscut or off-cut angle is +/−17 degrees from the m-plane towardsc-plane or alternatively at about the {20-21} crystal orientation plane.As another example, the present device includes a laser stripe orientedin a projection of the c-direction, which is perpendicular to thea-direction (or alternatively on the m-plane, it is configured in thec-direction). In one or more embodiments, the cleaved facet would be thegallium and nitrogen containing face (e.g., GaN face) that is +1-5degrees from a direction orthogonal to the projection of the c-direction(or alternatively, for the m-plane laser, it is the c-face).

As shown, the present device can be enclosed in a suitable package. Suchpackage can include those such as in TO-38 and TO-56 headers. Othersuitable package designs and methods can also exist, such as TO-9 andeven non-standard packaging. In a specific embodiment, the presentdevice can be implemented in a co-packaging configuration such as thosedescribed in U.S. Provisional Application No. 61/347,800, commonlyassigned, and hereby incorporated by reference for all purposes.

In other embodiments, the present laser device can be configured in avariety of applications. Such applications include laser displays,metrology, communications, health care and surgery, informationtechnology, and others. As an example, the present laser device can beprovided in a laser display such as those described in U.S. Ser. No.12/789,303 filed May 27, 2010, which claims priority to U.S. ProvisionalNos. 61/182,105 filed May 29, 2009 and 61/182,106 filed May 29, 2009,each of which is hereby incorporated by reference herein. Of course,there can be other variations, modifications, and alternatives.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A method for forming an optical devicecomprising: providing a gallium and nitrogen containing member having anm-plane nonpolar crystalline surface region characterized by a laserstripe region overlying a portion of the m-plane nonpolar crystallinesurface region, the laser stripe region being characterized by a cavityorientation substantially parallel to a c-direction, the laser striperegion having a first end and a second end; forming a pair of facetsincluding a first c-face facet provided on the first end of the laserstripe region and a second c-face facet provided on the second end ofthe laser stripe region; and subjecting the first c-face facet to adeposition process.
 2. The method of claim 1 wherein the depositionprocess includes coating the first c-face facet with a reflectivematerial; and wherein forming the pair of facets comprises separatelyforming the first c-face facet and the second c-face facet.
 3. Themethod of claim 1 wherein the pair of facets is formed before asingulating process; and wherein the m-plane nonpolar crystallinesurface region is characterized by an off-cut orientation of about −1degree towards (0001) and less than about 0.3 degrees towards (11-20).4. The method of claim 1 wherein the optical device is configured assingle lateral mode optical device or a multi-mode optical device. 5.The method of claim 1 wherein the optical device is characterized by awall plug efficiency of 14% and greater.
 6. The method of claim 1wherein the optical device is characterized by a wall plug efficiency of18% or 20% or 23% and greater.
 7. The method of claim 1 furthercomprising maintaining the second c-face facet as substantially exposedgallium and nitrogen containing material.
 8. The method of claim 1wherein the first c-face facet and the second c-face facet are cleavedfacets.